The present invention relates to a process for recovering precious metals from spent catalyst materials. Generally, in chemical industries, especially in the petrochemical industry, petroleum refining industry and the soap and detergent industry, a great amount of precious metal catalysts such as platinum and palladium are used. Further, the catalytic converter pollution control devices required on automobiles in recent years have contained precious metal catalysts such as platinum and palladium. These catalysts are generally employed in the form of supported catalysts wherein the precious metal is carried on the surface of a support or carrier composed of an inorganic ceramic material of an oxide such as aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide or combinations thereof. There exists a need for economical processes for completely recovering the precious metal catalytic components from spent catalysts. Recovery of such materials both provides for recycling of valuable components and reduces the potential environmental pollution caused by their disposal.
Several prior processes for recovering precious metals have been proposed which utilize leaching processes for recovery of the precious metal. These processes generally comprise a leaching process that removes the catalytic material by its chemical combination with another material in the gaseous or liquid phase. Representative of such processes may be considered U.S. Pat. No. 3,951,648 to Stern et al and U.S. Pat. No. 2,860,045 to Nixon et al and U.S. Pat. No. 3,469,971 to Leopard. These processes have the disadvantages that the precious metals are not totally recovered, the carrier for the precious metal is not utilized for another purpose and the materials used in the recovery are expensive and environmentally difficult to handle.
U.S. Pat. No. 4,142,871 to Zeiringer discloses a process for utilizing spent catalysts in a process which combines the formation of alumina abrasives with the recovery of nickel or cobalt materials from the catalysts. The Zeiringer process melts the catalyst material containing the heavy metal, cools the material and mechanically separates the alumina-containing melt component from the metal alloy residue.
U.S. Pat. No. 4,029,495 to Hirayama also discloses a process for separating heavy metal materials such as nickel and cobalt from spent catalyst support materials. In the process, the spent catalyst material is heated to a sintering temperature to cause aggregation of the metal component. The mixture then may be either crushed and separated or further heated to from 1480.degree. to 1580.degree. C. to separate the molten heavy metal phase and a second melted phase comprising the carrier. The carrier may be separated by pouring off the top layer for use in formation of ceramic fibers and pouring the bottom layer into a mold to form ingots.
There remains a need for an economical process of separating precious metals from carrier materials. There is particularly needed a method of separating, economically, very low concentrations of these metals such as 0.2% to about 0.01%. Further, there is a need for a process which enables utilization of spent catalysts for recovery of precious metals without creating waste materials which must be disposed of after precious metal recovery.